Optical spectroscopy measures the interaction of light, especially monochromatic light with a material to produce a spectrum characteristic of the material. Such interaction includes inelastic scattering processes, such as Raman and Brillouin scattering, and fluorescence emission process. Optical spectroscopy has been demonstrated to be a powerful non-invasive analytical technology for material characterization and identification.
Conventional optical spectroscopy generally utilizes a well-focused laser beam to produce inelastic scattering and/or fluorescence signal from the sample. This approach has the apparent advantage of relatively high efficiency in signal excitation and collection. However, it also suffers from the following drawbacks. First, only a small volume of the sample is measured. Thus the collected optical spectra may not be very representative, especially for some non-uniform samples. Second, the tightly focused laser beam may cause damage to some delicate samples. Third, for diffusely scattering samples which are not transparent to the laser beam, this approach will only measure the inelastic scattering and/or fluorescence signal from the surface layer of the sample. The majority of the material underneath the surface will be almost completely out of reach.
There thus exists a need for an improved light delivery and collection device for performing optical spectroscopy, which not only allows the measurement of a large area of the sample but also enables sub-surface optical signal excitation and collection.